The conversion of antigenic proteins into peptides that are presented by MHC products is one the central events leading up to an immune response. Protective immunity against pathogens such as viruses often requires the induction of both cytotoxic (CD8+) and helper (CD4+) T cell responses, restricted by MHC Class I and Class II products respectively. Whereas Class I molecules acquire most of their peptides from proteins synthesized in the cytosol, Class II molecules cover their need for peptides by sampling the endocytic pathway. A successful vaccine strategy for HIV must therefore target both presentation pathways to afford maximum protection. Especially activation of CD8+ cytotoxic T cells by exogenously administered subunit vaccines will be a challenge. Recent results obtained with the heat shock proteins grp94/gp96 and genetic fusions of Hsp70 with antigenic protein fragments derived from HIV suggest that the heat shock protein family may be successful in allowing entry of antigenic materials into the Class I presentation pathway in the absence of any adjuvants, and seemingly without the need for cytosolic synthesis of these antigenic entities. The mechanisms by which grp94/gp96 and Hsp70-SIV fusions accomplish this feat are altogether unclear, and will be explored in the present application with the methods of biochemistry and cell biology. In the present proposal we will study heat shock proteins as potentiators of an immune response and as a basis for subunit-based as well as DNA vaccines for induction of memory T cell responses. It is expected that detailed insights into how these heat shock proteins interact with MHC products, with components of the antigen presentation machinery, and with antigen presenting cells such as dendritic cells will allow the formulation of more effective antigen preparations that could serve as vaccines.